Expose mongo port in other container - mongodb

Question

I have this (custom) container which runs a java program which requires mongo locally. Now, with docker I would like to setup mongo in its own container. So I guess, in order to expose this 27017 port locally in this java-container I need to setup an SSH-tunnel, right ? If there is a easier way please let me know.
So, there is this official mongo image image, but I get the impression ssh is not install or running. What would be the best approach to do this?
UPDATE: I've rephrased the question more focussed on port-forwarding here

Answer 1

You have to make your container run on the same network. No need to ssh into your mongo or app container.
https://docs.docker.com/engine/userguide/networking/
First define a network
docker network create --driver bridge isolated_nw
Start you containers using that newly network
docker run -p 27017:27017 --network=isolated_nw -itd --name=mongo-cont mongo
docker run --network=isolated_nw -itd --name=app your_image
The image of mongo includes EXPOSE 27017 so from your app container, you should be able to access to the mongo container using its name mongo-cont

Answer 2

You can build your custom image on top of mongodb official image, which gives you the flexibility to install additional required packages.
FROM mongo:latest
RUN apt-get install ssh
Also try to use docker-compose to build and link your containers together, it will ease the process greatly.
version: '2'
services:
mongo:
image: mongo:latest
ports:
- "27017"
custom_project:
build:
context: . # Parent directory address of Dockerfile
dockerfile: Dockerfile-Custom # Name of Dockerfile
command: /root/docker-entrypoint.sh
This is the image used for mongodb official image.

Answer 3

You are trying to SSH into your container to gain access to it, but that isn't how you connect. Docker provides functionality to securely connect via the following methods.
Connect into a running container - Docs:
docker exec -it <container name> bash
$ root#665b4a1e17b6:/#
Start a container from image, and connect to it - Docs:
docker run -it <image name> bash
$ root#665b4a1e17b6:/#
Note: If it is an Alpine based image, it may not have Bash installed. In that case using sh instead of bash in your commands should work. Mongo's Dockerfile looks to use debian:jessie which will have bash support.